1. Field of the Invention
Composite materials having favorable acoustic and vibration damping properties, while improving other composite mechanical properties, are disclosed. In particular, composite materials that contain multilayered nonwoven interlayers of nonwoven with a compositional gradient are useful, for example, in structures found in aircrafts, such as fuselage skins, stringers and frames. Also contemplated are methods of making the composite material and the structures and aircrafts that contain the composite material.
2. Description of the Related Art
Fiber-reinforced polymer matrix composites (PMCs) are high-performance structural materials that are commonly used in applications requiring resistance to aggressive environments, high strength, and/or low weight. Examples of such applications include aircraft components (e.g. tails, wings, fuselages, propellers), boat hulls, and bicycle frames. PMCs may comprise layers of fibers that are bonded together with a matrix material, such as a polymer resin. The fibers reinforce the matrix, bearing the majority of the load supported by the composite, while the matrix bears a minority portion of the load supported by the composite and also transfers load from broken fibers to intact fibers. In this manner, PMCs may support greater loads than either the matrix or fiber may support alone. Furthermore, by tailoring the reinforcing fibers in a particular geometry or orientation, the composite can be efficiently designed to minimize weight and volume.
Numerous processes have been developed for the manufacture of PMCs. Examples may include wet layup, prepregging, and liquid infusion. In wet layup, the reinforcing fiber is wet with the matrix material, placed into a mold cavity, and allowed to harden or cure. This process may be performed in an automated fashion, such as with a chopper gun or a machine that receives dry fiber rolls, runs them through a resin dip bath, and places the wetted fibers in the mold. Alternatively, the resin may be applied manually using brushes.
In prepregging, composite components are fabricated with pre-impregnated woven fabrics or prepregs. The reinforcing fibers are impregnated with the matrix resin in a controlled fashion and frozen in order to inhibit polymerization of the resin. The frozen prepregs are then shipped and stored in the frozen condition until needed. When manufacturing composite parts from prepregs, the prepregs are, thawed to room temperature, cut to size, and placed in the mold cavity. Once in place, the prepregs are vacuum bagged and cured under pressure to achieve the required fiber volume fraction with a minimum of voids.
The use of advanced composite materials has gained wide acceptance over the last few decades because of their high strength-to-weight and stiffness-to-weight ratios. Advanced composite materials show higher stiffness but inferior damping performance and compared with metals and metal-matrix composites. Thus, there is a need for advanced composite materials having an enhanced damping capacity of a composite structural system with little reduction in stiffness and strength.
U.S. application Ser. No. 12/683,105 (Publ No. 20100170746), which is issued to the same assignees as the present application, is directed to a composite material comprises a nonwoven layer having a viscoelastic interleaf, which may be positioned mid-ply therein. Although this material has improved acoustic and vibrational damping properties over the conventional materials there is a need in the industry for a material with acoustic and vibrational damping properties and concomitantly improved composite mechanical properties such as delamination strength to advance the technology and satisfy customers. In addition it would be useful if the acoustic and vibrational damping properties could be achieved without plasma treatment, which is a complex, expensive and potentially aggressive treatment that may have a potentially detrimental effect on other mechanical properties.